Snowmobile Fanatics banner

1 - 19 of 19 Posts

·
Registered
Joined
·
172 Posts
Discussion Starter #1
Hey guys, got a problem here. I have a '97 Indy 500 SKS liquid. She ran the Iron Dog Pro Class in '97 & I picked it up for a song. It ran beautifully until about 2000, when it began bogging on low end. Keep the RPMs up and there was no stopping it. Higher Temperature and higher altitude would make it bog much worse, to the point where I simply had to turn around on a few trips and head back. I finally blew a piston in it at 12,000 miles, due to a crack in the carb boot. I bored it out .020 over & had both clutches rebuilt by a buncha knuckleheads at the local Polaris shop - I've had bad experiences there and I suspect that the clutches didn't have everything done to them that I paid for.
The track was toast as well, so I put a 1.75" paddle on it, and had to drop the drivers on the axle from 9-lug to 8-lugs.
I figured my bogging problems were over - NOPE! It bogs just as bad. Here's the funny thing - at 15 degrees, she runs like a top, plenty of power, no complaints. At 30 degrees, it's the biggest dog you've ever seen, to the point that I have to get off it and push it to get it going. When it's having it's normal bog-fest, I have to "feather" the throttle & let it catch up to itself, and you can feel / hear the engine ready, and THEN if I nail it, she takes off like it did when it was new. Top end power is all it has; any low end power disappears after it gets up to operating temp. Unless it's 15 degrees or colder, then it runs great.
I only run premium fuel in it, I know the gas isn't the problem. The clutch engages at 3,000, and it idles at about 1,000 until it warms up and then it gets lower and lower until it won't idle anymore. Temperature seems to be the key here...??
I've been beating my head against the wall trying to figure this one out, to no avail. Anyone got any ideas?
Thanks in advance!
 

·
Registered
Joined
·
2,573 Posts
WOW...OK...um...wish I could give you more, but I'd start out w/ the clutches. Sounds like you may have a problem there. After that I'd go to the carbs. Could be something simple like clogged fuel pick-up in the tank or airbox plugged. Definitely go with the clutches first, it may not fix it, but it should help; I'm thinkin' you've got a couple problems here, not just one. Let us know!
 

·
Registered
Joined
·
608 Posts
You have a carb problem. I would cean the carbs and if that isn't the trick, jet it down. Your idle should be higher, but wait untill you get it going good before you adjust it. At what Rpm does it come alive? Check the sparkplugs after it has idled for a minute. Let us know if they are wet and if one is worse than the other. Oh by the way welcome to the site. We will help you through your problem, you don't have to ride the way it is.
 

·
Registered
Joined
·
8,842 Posts
I agree that it could be a carb problem. if it ran the iron dog, maybe it is jetted for -40, running at 30 above you couldnt ride it hard enough to run clean. You can get the specs from polaris, for the temp and altitude you are running.
when you bored your engine out did some one reset the port highth? if not you have lost a little hp. if it was my sled i would most deffinatly have some one reset the ports to polaris spec, it makes unreal difference.
 

·
Registered
Joined
·
2,770 Posts
You need to jet that thing for different temps, stock is 250 main, 40 pilot.
On my 500 XC, I use the stock jet all the time, and just move the needle up and down for different temps, but I do that because they are flatslides, and it's easier than changing jets.
Warmer air is less dense and requires less fuel so smaller main jet.
Cold air is very dense, and requires more fuel, so bigger jet.
Ideally they should be a nice cardboard brown, or darker to be on the safe side of rich.
Check your plugs after a mile or 2, if white, too lean, bigger jet, more fuel...if black, too rich, smaller jet, less fuel.
Plugs don't lie when it comes to fuel to air mixtures.
If she is boggy in the bottom end, you might need to play with the pilot jet too, but as a rule, pilot jets do not need to be changed.

Here is a manual for tuning your carbs:

http://www.mikuni.com/pdf/vmmanual.pdf

Good luck.
 

·
Registered
Joined
·
172 Posts
Discussion Starter #6
Thanks for the responses, I really appreciate your help.

The jets were my first suspect, and you're right, it was jetted for running top end at very low temperatures. The chart calls for 330s for the area I normally ride in, when I first got it, it had 380s in it. I dropped jetting to 340s, still bogging. I put 310s in it, and that's when I blew the piston on it. It was due to the crack in the carb boot I told you about earlier, but still, it makes me paranoid to lean it out.
The plugs tell me it's running correctly with the 340 jets, it's a nice reddish-brown color on both plugs. However, they get black in a hurry if I let it idle. Both are firing, neither one is wet at any time... I thought about the spark as well, but the coil either works or it doesn't, right? I haven't checked the output of the coil, all I've done is have a buddy pull her over as I watched to see how the spark looks, and it appears to be normal spark for both plugs.
As far as what RPMs it comes alive at, usually it's about 5,000. Bog city at any RPMs below that.
It doesn't make sense to me why it would run decent when the engine is cold, but as it gets up to operating temp it loses all low end power.
I've never heard of resetting my port height, can you please explain what you mean? Polishing the intake ports? I didn't have anything done to the intake manifold or the head, I just took the jugs in to get them punched out.
 

·
Registered
Joined
·
246 Posts
I had this problem on my 700 MM when I left the gas in the tank over the summer causing the pilot jet to become pluged. (dumb me) Try running a little injector cleaner in you next tank of gas, about 1/2 bottle to a tank. It sounds like your problem is a bit worse then mine was so you may have to do it for a couple of tanks.

Last year mine was doing the same thing on the first ride of the year. It took about 25 miles of taking it easy then I had to get on it to stop a friend because he took a wrong turn on the way into my cabin but it finnaly blew it self out and ran like a champ the rest of the weekend.

BTW welcome to the Forum its good to see more Alaskans here.
 

·
Registered
Joined
·
172 Posts
Discussion Starter #9
I'm in Wasilla, commuting to Anchorage every day. Mostly do my riding up in Talkeetna, we've got a cabin 20 miles up the Talkeetna River.
Thanks for the tip on the pilot jet, I haven't investigated that yet. Many thanks for the tips, everyone!
Where are you located, In Alaska?
 

·
Registered
Joined
·
2,770 Posts
Originally posted by NightTrain
[br]
The plugs tell me it's running correctly with the 340 jets, it's a nice reddish-brown color on both plugs.
....Polishing the intake ports
You didn't say anything about jetting in the first post, so I assumed that was the prob, but sounds like you have a good handle on your mixture.
I think that injector cleaner is a good idea, but why not just tear down the carbs and clean them, quicker and more thorough than just dumping cleaner in your tank.
I think that a port and polish would be a good idea for over the summer though.
 

·
Registered
Joined
·
172 Posts
Discussion Starter #11
500fasEnuf : Thanks for the link for the Mikunis, I think that's just what the doctor ordered. I'll strip those down again, there were a couple of areas that I missed that I can see now that I have the manual for the carbs. I'm going to take a copy of that and leave it at the cabin to prepare for future carb misadventures.
 

·
Registered
Joined
·
2,770 Posts
Always happy to pass on a helpful link, NT.
BTW: genesis of NightTrain?? Bike??
 

·
Registered
Joined
·
172 Posts
Discussion Starter #13
Nope, it's always been my online handle, I picked it when I was a kid in high school Computer Science about '89 from the G-N-R song "NightTrain"... shows what I thought was really cool back then... lol
 

·
Registered
Joined
·
287 Posts
I know I preach this a lot on this board, but it really is better to just replace the pilot jets than to try to clean them. They are just too small to clean them 100%. Save yourself the aggravation and spend the $5 (US) to replace the pilots. You won't regret it.
 

·
Registered
Joined
·
172 Posts
Discussion Starter #15
That's a good idea, you're right - for $5 it's not worth screwing around with. Thanks!
 

·
Registered
Joined
·
608 Posts
You also may need to drop down a size on the pilot jets. I would leave the 340 mains in though. The mains control the top end fuel circuit and the pilots control the low end. You can also adjust the pilot air screw to adjust idle fuel mixture.
 

·
Registered
Joined
·
172 Posts
Discussion Starter #17
Thanks, ZA. Do you know where I can get a guide for adjusting the pilot air screw and is there a danger of running too lean on the low end by dropping a size on the pilot jets, or is the "Too Lean" danger mostly on top end? I don't want to lean her down too much and melt it down again. It was good practice rebuilding it last time, I don't wanna make it a habit! lol
 

·
Registered
Joined
·
608 Posts
Your melting danger is at high RPMs. Hard starting is the only thing that may happen if you are too lean. As far as the pilot air screw: turn them in untill they lightly bottom out (count the turns) and turn them counterclockwise about 1 1/2 turns. If this is where they were trygoing 2 turns out. In case you weren't sure the pilot screw is the small slotted screw on the right side of carb toward the back. All of my directions are as viewed as sitting on the sled. One more note: The more you turn the screw out the leaner it gets and in = richer. hHope this helps, but try the air screw before you change jets.
 

·
Registered
Joined
·
172 Posts
Discussion Starter #19
Allllrighty then!

The pilot jet was plugged on both carbs. Used 1.5 cans of parts cleaner, blew everything out and she runs great! No snow here, so the wife is going to be pissed when she sees what I did to the driveway and part of the lawn.. pulls the skiis right off the ground like it did when it was new.
News Flash : Paddle tracks are hell on grass!
Thanks for all the help guys, I didn't even know that pilot jet was there!
NT
 
1 - 19 of 19 Posts
Top